Conventionally, a direct conversion type radiation detector which converts radiation directly into carriers (charge information) in a semiconductor layer applies a predetermined bias voltage to a common electrode formed on a front surface of the semiconductor layer which is sensitive to radiation, and collects the carriers thereby generated in the semiconductor layer in pixel electrodes formed on a back surface of the semiconductor layer. Further, the carriers collected are read as radiation detection signals, using an active matrix substrate, thereby to detect the radiation.
Where an amorphous semiconductor layer such as a-Se (amorphous selenium), in particular, is used as the radiation sensitive semiconductor layer, a large and thick semiconductor layer can be formed easily by a method such as vacuum vapor deposition. Thus, the amorphous semiconductor layer can be constructed as a radiation conversion layer of a two-dimensional array type radiation detector.
Since the direct conversion type radiation detector applies a high voltage to the common electrode, a discharge occurs along the surface of the amorphous semiconductor layer. In order to solve the problem of this creeping discharge, in Patent Document 1 and in FIG. 4, entire surfaces of an amorphous semiconductor layer 44, a common electrode 42 and a carrier selective high resistance film 43 are covered with a curable synthetic resin film 53 (epoxy resin) acting as an insulating layer of high withstand voltage.
Further, Patent Document 1 also indicates a problem that solvent components of the epoxy resin react with a-Se forming the amorphous semiconductor layer 44, to discolor the surface of the amorphous semiconductor layer 44, and lower the withstand voltage. So, the entire surface of the amorphous semiconductor layer 44 is covered with the solvent-resistant and carrier selective high resistance film 43 such as Sb2S3 film, to reduce the reaction between the solvent components of the epoxy resin and a-Se and to prevent discoloration of the surface of the amorphous semiconductor layer 44 and lowering of the withstand voltage.
In order to avoid warpage and cracking of the radiation detector 40, the curable synthetic resin film 53 of high withstand voltage is fixed as pinched between an insulating substrate 51 and an insulating auxiliary plate 54 with a thermal expansion coefficient comparable to that of the insulating substrate 51.    [Patent Document 1]    Unexamined Patent Publication No. 2002-311144